This invention relates generally to flared tube fittings and tube couplers. More specifically, the present invention relates to a resilient sealing boot having a frusto-conical skirt disposed between facing frusto-conical sealing surfaces, wherein the skirt includes at least one O-ring sealing means which sealingly engages at least one of the frusto-conical sealing surfaces to prevent fluid flow.
In the past, considerable difficulty has been encountered in forming a fluid-tight joint between the flared end of a tube and a coupling member with which the tube flare is engaged when the coupling member and the tube are made of hard and tough materials such as certain grades of stainless steel. With such hard and tough materials, irregularities on the mating surfaces of the tube flare and the coupling member cannot be "ironed" out as occurs with tubes and coupling members made of metals such as copper, brass, aluminum, aluminum alloy, etc. The aforesaid leakage problem may be alleviated to some extent by accurately forming and polishing the mating surfaces, but this expedient is much too expensive to be any commercial value. Moreover, because drawn tubing is employed most frequently, it is likely that the inside surface will have lengthwise extending scratches or imperfections. Of course, hairline scratches or other imperfections on the inside of the tube flare may also result from the flaring operation.
Attempts to solve the above-noted leakage problem include the employment of a washer of ductile material introduced between the mating surfaces of the tube and the fitting, use of gasket-like crushable sealing washers, or, as mentioned above, the machining of extremely smooth finishes on mating parts. See, for example, U.S. Pat. Nos. 3,139,294 and 3,411,812. Although under some circumstances these prior solutions have satisfactorily solved the leakage problems, there are conditions under which prior sealing washers have not performed well. For example, in attempting to extend the use of flared tube fittings to encompass low molecular weight gases, such as hydrogen and helium, at cryogenic or elevated temperatures and high or low pressures, the leakage problem has become acute.
Accordingly, there has been a need for an improved tube coupler that utilizes, insofar as possible, standard coupling components, and yet eliminates fluid leakage therebetween. Preferably, such an improved tube coupler would simply interpose a novel sealing boot between the flared end of a tube and the coupling member in order to eliminate any leakage between facing sealing surfaces. Such a sealing boot should provide a reliable, non-fragile point contact seal which overcomes the drawbacks of prior gaskets, and should be constructed of a material resistant to chemical or temperature degradation. The sealing boot must be of simple construction, economical, and adaptable to various uses and requirements. The present invention fulfills these needs and provides other related advantages.